Convert contents of array into index

Hello,

I have an array. 1x3127 double which contains the indexes of another array. I want to use those index values to index another array and make those points =0

So for example,

col = [21 34 56 78 54 99];
l(col) = 0;    % where l is another array for which I want l(21),l(34),l(56) = 0 etc.

I tried using the following code snippet but it does not work.

col = find(l<0);
   for ii = 1:length(col)
       a= cell2mat(ii);
       l(a) = 0;
   end

Please help! Thanks!

Answer 1

[Alexandra Harkai]

Your first code should work.

l = ones(1, 10000); % make sure this is bigger than the largest index col will specify
col = [21 34 56 78 54 99];
l(col) = 0; % this makes the 21st, 34th, 56th, etc. elements 0

[Alexandra Harkai]

Your second code does not work because col is not used anywhere.

col = find(l<0);       % this is a 0-1 vector, 1 indicating where l has a negative element
for ii = 1:length(col) % length of col is the number of negative elements in l
  a = cell2mat(ii);    % this doesn't use col at all
  l(a) = 0;            % so this puts the 0s in the wrong places
end

This essentially counts how many negative elements are there in vector l (let's say n), then changes the first n elements of l to 0.